mm: count writeback pages per BDI

Count per BDI writeback pages.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 11 insertions, 2 deletions

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index bfae09d2a1eb..4d9222c2f222 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -28,6 +28,7 @@ typedef int (congested_fn)(void *, int);
 
 enum bdi_stat_item {
         BDI_RECLAIMABLE,
+        BDI_WRITEBACK,
         NR_BDI_STAT_ITEMS
 };
 
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 9b3c4ee62abf..f1d201fdcf9c 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -979,14 +979,18 @@ int test_clear_page_writeback(struct page *page)
         int ret;
 
         if (mapping) {
+                struct backing_dev_info *bdi = mapping->backing_dev_info;
                 unsigned long flags;
 
                 write_lock_irqsave(&mapping->tree_lock, flags);
                 ret = TestClearPageWriteback(page);
-                if (ret)
+                if (ret) {
                         radix_tree_tag_clear(&mapping->page_tree,
                                                 page_index(page),
                                                 PAGECACHE_TAG_WRITEBACK);
+                        if (bdi_cap_writeback_dirty(bdi))
+                                __dec_bdi_stat(bdi, BDI_WRITEBACK);
+                }
                 write_unlock_irqrestore(&mapping->tree_lock, flags);
         } else {
                 ret = TestClearPageWriteback(page);
@@ -1002,14 +1006,18 @@ int test_set_page_writeback(struct page *page)
         int ret;
 
         if (mapping) {
+                struct backing_dev_info *bdi = mapping->backing_dev_info;
                 unsigned long flags;
 
                 write_lock_irqsave(&mapping->tree_lock, flags);
                 ret = TestSetPageWriteback(page);
-                if (!ret)
+                if (!ret) {
                         radix_tree_tag_set(&mapping->page_tree,
                                                 page_index(page),
                                                 PAGECACHE_TAG_WRITEBACK);
+                        if (bdi_cap_writeback_dirty(bdi))
+                                __inc_bdi_stat(bdi, BDI_WRITEBACK);
+                }
                 if (!PageDirty(page))
                         radix_tree_tag_clear(&mapping->page_tree,
                                                 page_index(page),